In conventional photographic coatings, emulsions, dispersions, and other photographic addenda for each speed or color separation layer are coated from fluid gelatin solutions, called melts or coating melts. Usually, coating takes place at temperatures between about 35.degree. to about 50.degree. C.
Generally, in the photographic art there are two primary methods of coating photographic materials. One is the bead coating process. U.S. Pat. No. 2,761,417 --Russell et al, U.S. Pat. No. 2,681,294--Beguin, and U.S. Pat. No. 4,525,392--Ishizaki, illustrate simultaneously applying multiple layers of photographic materials by the bead coating process, and apparatus for practicing that process.
The second primary method is the curtain coating process. U.S. Pat. No. 3,632,374--Greiller, and U.S. Pat. No. 4,569,863--Koepke et al, illustrate apparatus and process for curtain coating.
It is well known that adjustment and control of viscosities of melts of individual layers can improve layer thickness uniformity of finished coated products. It is also known that layer viscosities outside optimum ranges may cause undesired variations in layer thickness during flow on the slides of the coating hopper or on a non horizontal web path after coating.
Certain photographic addenda such as masking couplers, oxidized developer scavengers, filter dyes, optical brighteners, ultraviolet radiation absorbers, dye transfer dyes, etc., when admixed in a melt comprising gelatin, produce excessively high viscosity, which leads to problems as described above. Such photographic addenda are in general molecules with large hydrophobic groups and are usually solubilized with one or more fully ionized anionic groups, such as -SO.sub.3.sup.- (i.e., sulfonate) groups, sulfate groups or carboxy groups. Such materials are usually fully water soluble, or are soluble to the extent of about 5-20% by weight, in water containing 5 to 20% by weight of a water miscible auxiliary solvent such as methanol, ethanol, propanol, isopropanol, acetone, methyl ethyl ketone, ethyl acetate, or the like. Such materials behave also in a similar manner in the presence of gelatin.
It has been known from U.S. Pat. No. 3,409,435, that certain amphiphilic addenda, such as polyalkylene oxide block oligomers or polymers, when added to melts containing the mentioned viscosity-increasing photographic addenda, produce moderation of melt viscosity. Such amphiphilic addenda of the prior art (U.S. Pat. No. 3,409,435) can be defined as follows, and are illustrated by the representative structures of such compounds shown in Table I below:
Block oligomeric compounds comprising hydrophobic polyoxypropylene blocks (A) and hydrophilic polyoxyethylene blocks (B) joined in the manner of A-B-A, B-A-B, A-B, (A-B).sub.n .ident.G.ident.(B-A), or (B-A).sub.n .ident.G.ident.(A-B), where G is a connective organic moiety and n is between 1 and 3.
TABLE I __________________________________________________________________________ Representative Structures of Prior Art Amphiphilic Compounds Used in Melt Viscosity Control Name Molecular ID (Manufacturer) Best Known Structure Weight Range __________________________________________________________________________ PA-1 Pluronic .TM. Polyols (BASF)* ##STR1## 1,100 to 14,000 a = 1-128, b = 16-69, and c = 1-128 PA-2 R Polyols (BASF) ##STR2## 1,900 to 9,000 a = 8-268, b = 43-204, and c = 8-268 PA-3 Plurodot .TM. Polyols (BASF)* Liquid Polyethers Based on 3,200 to 7,500 Alkoxylated Triols PA-4 Tetronic .TM. Polyols (BASF)* ##STR3## 3,200 to 27,000 x = 2-31 and y = 7-491 __________________________________________________________________________ *Pluronic L44 Polyol, a = c = 10; and b = 20.
Other examples of such amphiphilic addenda of prior art can be found in Ono et al. U.S. Pat. No. 3,860,425 (1975).
However, such prior art materials that contain a large number of polyalkylene oxide groups produce adverse photographic effects in some photographic products, as will be demonstrated in one of the examples set forth in this application.
One of the ways of reducing high viscosities of melts is by dilution with water. However, such a procedure leads to increased water load in the drier, under high speed coating conditions, used for high volume film and paper products. Therefore, dilution is not always a desirable approach.
Therefore, there is a need for melt compositions which will produce photographic melts (of the aforesaid photographic addenda and agents) which have sufficiently low viscosity, and adequate gelatin concentration, such that no excessive drier wet load is encountered during manufacturing of photographic paper and film products, and such that no, or substantially no, adverse effect is produced on the desired sensitometric behavior of the photographic multilayer pack in question.